In 3rd Generation Partnership Project (3GPP) Release 12, the Long Term Evolution (LTE) standard has been extended with support of device to device (D2D) communications (e.g., “sidelink” communications) features targeting both commercial and public safety applications, as illustrated in FIG. 1. Some applications enabled by 3GPP Release 12 LTE are device discovery, where devices are able to sense the proximity of another device and associated application by broadcasting and detecting discovery messages that carry device and application identities. Another application consists of direct communication based on physical channels terminated directly between devices.
One of the potential extensions for the device-to-device (D2D) work consists of support for vehicle-to-anything (V2x) communication, which includes any combination of direct communication between a vehicle and another vehicle (V2V), a pedestrian (V2P), and infrastructure (V2I). V2x communication may take advantage of a network infrastructure, when available, but at least basic V2x connectivity should be possible even in case of lack of coverage. Providing an LTE-based V2x interface may be economically advantageous because of the LTE economies of scale and it may enable tighter integration between communications with the V2I, V2P, and V2V communications, as compared to using a dedicated V2x technology. V2x communications may carry both non-safety and safety information, where each of the applications and services may be associated with specific requirements sets (e.g., latency, reliability, capacity).
The European Telecommunications Standards Institute (ETSI) has defined two types of messages for road safety: Co-operative Awareness Message (CAM) and Decentralized Environmental Notification Message (DENM). A CAM message is intended to enable vehicles, including emergency vehicles, to notify their presence and other relevant parameters in a broadcast fashion. Such messages target other vehicles, pedestrians, and infrastructure, and are handled by their applications. The CAM message also serves as active assistance to safety driving for normal traffic. The availability of a CAM message is indicatively checked for every one hundred milliseconds (100 ms.), yielding a maximum detection latency requirement of no more than one hundred milliseconds (≤100 ms.) for most messages. A DENM message is event-triggered, such as by braking, and the availability of a DENM message is also checked for every one hundred milliseconds (100 ms.). Depending on the use case latency requirements for CAM and DENM may vary significantly. As an example, latency may vary from twenty milliseconds (20 ms.) for pre-crash warnings, to one hundred milliseconds (100 ms.) for emergency stops or queue warnings, or to one thousand milliseconds (1000 ms.) for non-safety related use cases such as traffic flow optimization and curve speed warnings. The package size of CAM and DENM message varies from 100+ to 800+ bytes and the typical size is around three hundred (300) bytes depending on the specific V2X use case, message type (e.g., DENM is supposed to be larger than CAM) and on the security format included in the packet (e.g., full certificate or certificate digest). The message is supposed to be detected by all vehicles in proximity.
The SAE (Society of the Automotive Engineers) also defined the Basic Safety Message (BSM) for DSRC with various messages sizes defined. According to the importance and urgency of the messages, the BSMs are further classified into different priorities. Sidelink transmissions (also known as D2D or ProSe) over the so-called PC5 interface (e.g., sidelink interface) in cellular spectrum have been standardized in 3GPP since 3GPP Release 12. In 3GPP Release 12, two different operative modes have been specified. In a first operation mode (mode-1), a user equipment (UE) in RRC_CONNECTED mode requests D2D resources and an eNodeB (eNB) grants them via a physical downlink control channel (PDCCH) (e.g., downlink control information 5, DCI5) or via dedicated signaling. In a second operation mode (mode-2), a UE autonomously selects resources for transmission from a pool of available resources that the eNB broadcasts via system information block (SIB) signaling for transmissions on carriers other than the primary cell (PCell) or via dedicated signaling for transmission on the PCell. Therefore, unlike the first operation mode, the second operation mode may be performed also by UEs in RRC_IDLE.
In 3GPP Release 14, the usage of sidelink is extended to the V2x domain. The design of the sidelink physical layer in 3GPP Release 12 has been dictated by the assumptions of a few number of UEs competing for the same physical resources in the spectrum, to carry voice packet for mission critical push-to-talk (MCPTT) traffic, and low-mobility. On the other hand, in V2x the sidelink should be able to cope with higher load scenario (i.e. hundreds of cars may potentially contend physical resources), to carry time/event triggered V2x messages (CAM, DNEM), and high mobility. For these reasons, 3GPP has discussed possible enhancements to the sidelink physical layer.
In order to properly exploit the available frequency resources, an eNB scheduler needs to execute resource allocation. In LTE, resource allocation decisions are taken on a transmission time interval (TTI) granularity which corresponds to one millisecond (1 ms.) Given a certain pool of available frequency resources and a certain amount of UEs connected to the cell, the scheduler may adopt different scheduling strategies to assign frequency resources to such UEs. Generally, the scheduler prioritizes the UEs according to the quality of service (QoS) requirement of different UE's traffic. For example, control plane signaling (e.g., RRC) is always prioritized over user plane data. Additionally, user plane data may be treated differently according to its QoS identifier (QCI) provided during data radio bearer (DRB) establishment. For instance, delay sensitive traffic (e.g., VoIP) may be subject to different scheduling policies than non-delay sensitive traffic (e.g., FTP/HTTP data streaming) so that delay sensitive traffic has a higher probability to fulfil certain latency constraints.
As previously described, V2X is also expected to be a delay sensitive and periodic type similarly to VoIP. Therefore, delay-aware schedulers would be a natural implementation solution to fit into the V2X framework. Among prior-art delay-aware schedulers, it is worth mentioning a delay-based scheduler (DBS) and a semi-persistent scheduler (SPS). DBS takes as input an estimation of the time spent by a certain packet in the downlink and uplink buffer (e.g., at UE), so that when a certain threshold is reached the packet gets higher priority and may be scheduled earlier than other packets in the buffer. In order to keep a better uplink buffer estimation, the DBS may use some traffic characteristics that are known a priori for that specific DRB (e.g., for VoIP, it is known that every twenty milliseconds (20 ms.) the UE generates a new Vol P packet).
Instead, SPS provides a semi-persistent resource allocation for UEs. This scheduling mechanism is specified in 3GPP and implies that the eNB configures via radio resource control (RRC) signaling a UE to use SPS resources with a certain configurable periodicity. The actual activation/release of SPS may be done dynamically via PDCCH (e.g., using a semi-persistent C-RNTI), which also indicates the frequency resources and the modulation and coding scheme to be used every nth subframe (e.g., as indicated in RRC configuration). SPS may also be re-activated meaning that a new PDCCH is transmitted carrying for a certain SPS configuration a different resource assignment (e.g., different PRB, MCS).
Further, multiple SPS configurations have been proposed. These multiple SPS configurations with different configuration parameters can be assigned by the base station to terminal devices. It has also been proposed to allow the multiple SPS configurations to be active simultaneously at one UE. In this case, the SPS configurations and UE assistance information may be linked to one or more radio bearers. However, such simultaneous activity of the multiple SPS configurations may cause collisions at the UE. In other words, the packets with these simultaneously active SPS configurations would collide in some subframes.
When such a collision occurs in a certain subframe, the terminal device or base station has to determine which SPS configuration should be used in the subframe. Such determination will result in tedious and inefficient use of network resources, as will be analyzed in the detailed description. At present, there is no effective or efficient proposal of how to utilize these SPS configurations at a terminal device in the V2x communications (e.g., via D2D sidelink or cellular uplink). Accordingly, there is a need for improved techniques for handling collisions between multiple semi-persistent grants. In addition, other desirable features and characteristics of the present disclosure will become apparent from the subsequent detailed description and embodiments, taken in conjunction with the accompanying figures and the foregoing technical field and background.
The Background section of this document is provided to place embodiments of the present disclosure in technological and operational context, to assist those of skill in the art in understanding their scope and utility. Unless explicitly identified as such, no statement herein is admitted to be prior art merely by its inclusion in the Background section.